Basically - 4 engines and gunners as described. Pilot and co-pilot. The co-pilot is normally the individual being stitched (soaked).
Commentator builds the crew/engines (pre-briefed) from the audience and narrates the story of the flight. Any short flight over water would do. The flight is attacked by bandits and the engines are lost one by one. Eventually, the crew glide into the oggin and at the point of impact, the skipper hands over the captaincy to the co as he jumps out the way and someone from the front row throws a bucket of water over the poor bugger as they "splash" into the sea.
Story telling ability and sound effects make it all the funnier, of course, copious amounts of beer help too.
I would like to add that it sounds very childish and not at all what I would expect from Her Majesty's finest - hang on, we're retired, have a blast.
tam